1. Field of the Invention
The present invention relates to a device for correcting the control quantity of an internal combustion engine at the time when the knocking is detected, by detecting the knocking of the internal combustion engine based on an ionic current that flows through a spark plug during the combustion in the internal combustion engine. More specifically, the invention relates to a device for controlling the knocking of an internal combustion engine by preventing erroneous judgement and erroneous control caused by a sharp increase in the background level during the transient operation in which the knocking occurs much.
2. Prior Art
In a device for controlling the knocking of an internal combustion engine, so far, it is accepted practice to judge the occurrence of knocking during the operation and, when the occurrence of knocking is detected, the control quantity for the internal combustion engine is corrected toward the side of suppressing the knocking (e.g., toward the side of delaying the ignition timing) depending upon the amount of knocking in order to prevent damage to the internal combustion engine.
In order to detect the knocking of the internal combustion engine, there has also been proposed a device that utilizes a change in the amount of ions produced during the combustion of the internal combustion engine.
The device for controlling the knocking of the internal combustion engine based on the ionic current is capable of detecting the intensity of knocking in each of the cylinders without using knock sensor, and is effective in decreasing the cost.
In the device of this type, a reference level for judging the noise (background level) is set for an ionic current detection signal in order to prevent erroneous detection of the knocking caused by noise superposed on the ionic current.
In a device disclosed in, for example, Japanese Patent Laid-Open No. 10-9108, a background level (reference for judging the noise level) operated from the sum of an average value of the detection signal intensities and an insensitive region (offset value) based on the operation condition, has been set for a signal that is obtained by shaping the waveform of a knock current detection signal.
FIG. 5 is a block diagram schematically illustrating a conventional device for controlling the knocking of an internal combustion engine. FIG. 6 is a timing chart illustrating the operation waveforms of signals in FIG. 5 and shows a case where a knock signal Ki is superposed on a waveform-shaped signal Fi of an ionic current detection signal Ei.
In FIG. 5, the ignition device 1 of the internal combustion engine includes an ignition coil having a primary winding and a secondary winding, and a power transistor (both of which are not shown) for interrupting the flow of the primary current il (see FIG. 6) into the ignition coil.
The power transistor in the ignition device 1 turns on and off (flows and interrupts) the primary current il to the ignition coil in response to an ignition signal P from an ECU 5, and the ignition coil generates a high ignition voltage V2 (see FIG. 6) through the secondary winding in response to the turn on and off of the power transistor.
Being impressed with a high spark voltage V2 from the ignition device 1, the spark plug 2 generates a spark to ignite the mixture at a predetermined timing in each of the cylinders of the engine.
That is, the spark plug 2 of a cylinder that is to be controlled is impressed with a high spark voltage in response to an ignition timing.
In order to detect the ionic current that flows across a gap of the spark plug 2 at the time of combustion, the ionic current detecting circuit 3 includes a bias means (capacitor) for applying a bias voltage to the spark plug 2 through the ignition coil in the ignition device 1, and a resistor (both of which are not shown) for producing an ionic current detection signal Ei.
Various sensors 4 include a known throttle opening sensor, a crank angle sensor, a temperature sensor and the like sensors, and produce various sensor signals that represent the operation conditions of the internal combustion engine. For example, the crank angle sensor which is one of the various sensors 4 produces a crank angle signal SGT (see FIG. 6) depending on the rotational speed of the engine.
Various sensor signals inclusive of the ionic current detection signal Ei and the crank angle signal SGT, are input to the ECU 5 that comprises a microcomputer.
The crank angle signal SGT has a pulse edge representing a reference crank angular position in each cylinder, and is used by the ECU 5 for executing various control operations.
The ECU 5 includes a knock detecting means 6 for detecting the knocking based on the ionic current detection signal Ei, and an ignition control means 7 that delays the spark signal P based on the result of detecting the knocking by the knock detecting means 6.
In order to form an ignition signal P based on the operation conditions from various sensors 4 and the result of judging the knocking by the comparator means 15, the ignition control means 7 includes an ignition timing calculating means for determining the ignition timing of the engine based on the operation conditions, and an ignition timing correction means that calculates the delay quantity corresponding to the detected amount of knocking of when it is judged that the knocking has occurred and reflects the delay amount on the ignition timing.
Not being limited to the ignition control means 7, the control quantity means for establishing the control quantity of the engine may be a fuel injection control means (not shown) that controls the amount of fuel injection and the injection timing. Further, the control quantity correction means for suppressing the knocking can work to delay the fuel injection timing.
The knock detecting means 6 in the ECU 5 includes a filter means 11 comprising a band-pass filter, a counter means 12, an averaging means 13, an offset means 14, and a comparator means 15.
The filter means 11 includes a waveform-shaping means, and picks up a knock signal Ki in a predetermined frequency band from the waveform-shaped signal Fi (see FIG. 6) of the ionic current detection signal Ei.
The counter means 12 includes a waveform-processing means, and counts the number N of the pulses of the knock signals Ki after their shapes have been processed.
The counter means 12 constitutes a knocking level operation means, and counts the number N of the pulses (signals of the knocking level) corresponding to the knocking state of the engine.
The number N of the pulses (signals of the knocking level) represents the amount of knocking occurring.
The averaging means 13 averages the number N of the pulses to operate an average knocking level AVE.
The offset means 14 offsets the average knocking level AVE and forms a background level BGL (reference for judging the noise level).
The offset means 14 includes an offset operation means for determining an offset value OFS for the average knocking level AVE depending on the operation conditions of the engine, and a background level operation means for determining the background level BGL by adding up the average knocking level AVE and the offset value OFS together.
The comparator means 15 constitutes a knock-judging means, and compares the number N of the pulses (signals of the knocking level) with the background level BGL to judge the knocking state of the engine. When the number N of the pulses exceeds the background level BGL, the comparator means 15 produces the result of comparison representing the occurrence of knocking.
Next, described below with reference to FIGS. 5 and 6 as well as a flow chart of FIG. 7 is the operation of the conventional device for controlling the knocking of the internal combustion engine.
First, the ECU 5 receives a crank angle signal SGT and the like signals from various sensors 4, executes various operations depending upon the operation conditions, and produces drive signals to various actuators such as the ignition device 1 and the like.
For example, the ECU 5 turns the power transistor in the ignition device 1 on and off in response to the ignition signal P to flow and interrupt the primary current il.
In this case, the bias power source (capacitor) in the ionic current detecting circuit 3 is electrically charged with the primary voltage V1 that generates in the ignition coil when the primary current il flows therein.
Further, the primary voltage Vl rises when the primary current il is interrupted (corresponds to an ignition timing of the engine), and a further elevated secondary voltage V2 (several tens of kV) is generated from the secondary winding of the ignition coil. The secondary voltage V2 is applied to the spark plug 2 of a cylinder in which the ignition is controlled to burn a mixture in the combustion chamber.
As the mixture burns, ions generate in the combustion chamber of the combustion cylinder, and a bias voltage electrically charged in the capacitor in the ionic current detecting circuit 3 is discharged through the spark plug 2 immediately after the ignition control.
The resistor in the ionic current detecting circuit 3 converts the ionic current into a voltage to produce it as an ionic current detection signal Ei.
Thus, the ionic current that flows through the spark plug 2 after the combustion is input as the ionic current detection signal Ei to the knock detecting means 6 in the ECU 5.
When the engine knocks, the knocking vibration components are superposed on the ionic current, and the waveform-shaped signal Fi of the ionic current detection signal Ei acquires a waveform on which the knocking vibration components are superposed as shown in FIG. 6.
Referring to FIG. 7 illustrating the operation for processing the ionic current detection signal Ei, the filter-means 11 of the knock detecting means 6 in the ECU 5 picks up the knock signals Ki only from the waveform-shaped signals Fi of the ionic current detection signals Ei (step S1).
The counter means 12 shapes the waveforms of the knock signals Ki to convert them into a knock pulse train Kp, and counts the number N of the pulses in the knock pulse train Kp (step S2).
The number N of the pulses is strongly related to the intensity of knocking and is used for judging the knocking as will be described later and is, further, used for updating the background level BGL in the next time.
That is, the comparator means 15 in the knock detecting means 6 compares the number N of the pulses with the background level BGL in the previous time, and judges whether the number N of the pulses is larger than the background level BGL (step S3).
The number N of the pulses increases with an increase in the intensity of knocking and, hence, the comparator means 15 judges the occurrence of knocking and the intensity of knocking based on the number N of the pulses.
When it is judged at step S3 that N&gt;BGL (i.e., YES), the ignition control means 7 operates a delay control quantity for delaying the ignition timing (for suppressing the knocking)(step S4). When it is judged at step S3 that N.ltoreq.BGL (i.e., NO), the ignition control means 7 operates an advance control quantity (step S5).
Here, the ignition control means 7, at step S4, makes a reference to the delay correction quantity in the ignition control of the previous time and of this time, and, at step S5, makes a reference to the delay correction quantity in the ignition control of the previous time, thereby to operate the control quantities.
When the state N&gt;BGL (knock is occurring) is consecutively judged at step S3, the delay quantities are successively added up, and are no longer added up at a moment when it is judged that no knocking is occurring.
The background level BGL (predetermined number of pulses) that serves as a reference for judging the knocking varies depending on the rotational speed of the engine and the level for shaping the waveforms of the detection signals Ei, but is set to a value of, for example, about 5 to about 20.
When the knocking is detected by the comparator means 15 based on the number N of the pulses, the control quantity is corrected toward the side of suppressing the knocking (i.e., the ignition is optimized for the cylinder in which the knocking is occurring) in order to effectively suppress the knocking.
On the other hand, the averaging means 13 in the knock detecting means 6 averages (filters) the number N of the pulses, and operates an average knocking level AVE by using the following formulas (1) and (2)(step S6). EQU AVE=AVE(n-1).times.KF+NP.times.(1-KF) (1) EQU NP=max{N-BGL(n-1),0} (2)
In the formula (1), AVE(n-1) is an average knocking level AVE of the previous time, and KF is an averaging coefficient (0&lt;KF&lt;1) and in the formula (2), BGL(n-1) is a background level BGL of the previous time.
The offset means 14 adds an offset value OFS to the average knocking level AVE to operate the background level BGL according to the following formula (3)(step S7), EQU BGL=AVE+OFS (3)
Finally, the ECU 5 stores the background level BGL operated according to the formula (3) in the offset means 14 as a reference for comparison for judging the knocking of when the ignition is controlled in the next time (step S8), and the processing routine of FIG. 7 ends.
Next, described below with reference to FIGS. 8 and 9 is the operation for detecting the knocking of when the average knocking level AVE has increased during the transient operation condition (accelerating or decelerating state).
In FIGS. 8 and 9, the abscissa represents the time and the ordinate (level in the form of a bar graph) represents the number N of the pulses, and there are shown the number Pn of the pulses corresponding to the noise level and the number Pk of the pulses corresponding to the knocking level.
In these drawings, further, the solid curves represent changes in the average knocking level AVE with the passage of time, dotted curves represent changes in the offset value OFS with the passage of time, and dot-dash chain curves represent changes in the background level BGL (=AVE+OFS) with the passage of time.
FIG. 8 illustrates changes with the passage of time of when the engine is shifted from a steady state into an accelerating state and is returned again to a steady state, wherein the offset value OFS (dotted line) increases with an increase in the rotational speed of the engine.
FIG. 9 illustrates changes with the passage of time of when the engine is shifted from a steady state into a decelerating state and is returned again to a steady state, wherein the offset value OFS (dotted line) decreases with a decrease in the rotational speed of the engine.
In FIG. 8, the background level BGL (level for judging the knocking) based on the number N of the pulses (signals of the knock level) in a steady state is changing relatively stably and properly.
When the pulses are detected in a number Pk corresponding to the knocking level, therefore, the knocking is properly judged relying on N&gt;BGL. Further, when the pulses are detected in a number Pn corresponding to the noise level, the noise is properly judged relying on N.ltoreq.BGL.
When the engine is shifted to the accelerating state as shown in FIG. 8, however, the knocking occurs frequently and, hence, the average knocking level AVE sharply rises and the background level BGL sharply rises, too, accompanying the average knocking level VE.
In the accelerating state, therefore, the background level BGL does not properly change, whereby the number Pk of the pulses of the knocking level becomes smaller than that of the background level BGL, and most of the pulses among those of the number Pk of the knocking level are erroneously judged as those of the noise level.
Similarly, even when the engine is shifted from the steady state to the decelerating state as shown in FIG. 9, the knocking occurs frequently. Therefore, the average knocking level AVE sharply rises and the background level BGL sharply rises, too.
Even in the decelerating state, therefore, the background level BGL does not properly change, and most of the pulses among those of the number Pk of the knocking level are erroneously judged as those of the noise level.
Even right after the engine is shifted from the decelerating state to the steady state, the average knocking level AVE that has increased during the deceleration does not decrease to a sufficient degree. Therefore, the number N of the pulses of the knocking level fails to exceed the background level BGL, and the pulses are often erroneously judged to be those of the noise level.
As described above, the conventional device for controlling the knocking of internal combustion engines has not been equipped with means for suppressing a quick increase in the average knocking level AVE caused by the frequent occurrence of knocking in the transient operation state. Therefore, the background level BGL sharply increases in the transient state making it difficult to correctly judge the knocking level, resulting in a decrease in the performance for controlling the knocking.